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Groups > comp.lang.c > #24112

Re: signal() anomaly

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On 2012-08-02, Stephen Sprunk <stephen@sprunk.org> wrote:
> On 01-Aug-12 13:58, hip cat wrote:
>> My code has a certain pointer that sometimes unexpectedly becomes null. 
>> It would be a lot of work to find every place the pointer gets 
>> dereferenced and add a null check. So I want to just ignore it by 
>> catching the signal.
>
> Sorry, but the correct solution is to check for null before you
> dereference a pointer, even if it is theoretically "impossible" for that
> pointer to be null.

Following this advice would make it impossible to dereference a pointer:

/* assuming pointer is non-volatile */

if (pointer != NULL)
{
  /* at this point it's theoretically impossible for pointer
     to be null, but let's check anyway */
  if (pointer != NULL)
  {
    /* at this point it's theoretically impossible for pointer
       to be null, but let's check anyway */
    if (pointer != NULL)
    {
      /* at this point it's theoretically impossible for pointer
         to be null, but let's check anyway */
      if (pointer != NULL)
      {
        /* at this point it's theoretically impossible for pointer
           to be null, but let's check anyway */
        if (pointer != NULL)
        {
          /* at this point it's theoretically impossible for pointer
             to be null, but let's check anyway */
          if (pointer != NULL)
          {
            /* at this point it's theoretically impossible for pointer
               to be null, but let's check anyway */

                /* ... etc ad infinitum ... */
  
                        do_something_with(*pointer);

                /* ... */
          }
        }
      }
    }
  }
}

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signal() anomaly hip cat <nospam@nospam.com> - 2012-07-31 20:13 +0000
  Re: signal() anomaly Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-31 16:35 -0400
    Re: signal() anomaly hip cat <nospam@nospam.com> - 2012-08-01 18:59 +0000
    Re: signal() anomaly Nick Bowler <nbowler@draconx.ca> - 2012-08-01 20:14 +0000
  Re: signal() anomaly falk@rahul.net (Edward A. Falk) - 2012-07-31 22:12 +0000
    Re: signal() anomaly hip cat <nospam@nospam.com> - 2012-08-01 18:58 +0000
      Re: signal() anomaly James Kuyper <jameskuyper@verizon.net> - 2012-08-01 15:33 -0400
        Re: signal() anomaly hip cat <nospam@nospam.com> - 2012-08-01 20:47 +0000
          Re: signal() anomaly Paul <nospam@needed.com> - 2012-08-01 17:34 -0400
            Re: signal() anomaly Johann Klammer <klammerj@NOSPAM.a1.net> - 2012-08-02 06:34 +0200
              Re: signal() anomaly Paul <nospam@needed.com> - 2012-08-02 07:10 -0400
          Re: signal() anomaly Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-01 18:07 -0400
            Re: signal() anomaly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-08-02 00:15 +0100
              Re: signal() anomaly Nick Bowler <nbowler@draconx.ca> - 2012-08-02 00:05 +0000
                Re: signal() anomaly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-08-02 02:47 +0100
          Re: signal() anomaly James Kuyper <jameskuyper@verizon.net> - 2012-08-01 18:13 -0400
          Re: signal() anomaly James Kuyper <jameskuyper@verizon.net> - 2012-08-01 18:14 -0400
          Re: signal() anomaly Nobody <nobody@nowhere.com> - 2012-08-02 12:52 +0100
      Re: signal() anomaly Angel <angel+news@spamcop.net> - 2012-08-01 19:41 +0000
      Re: signal() anomaly Kenneth Brody <kenbrody@spamcop.net> - 2012-08-01 16:16 -0400
      Re: signal() anomaly Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-01 16:33 -0400
      Re: signal() anomaly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-08-02 00:22 +0100
      Re: signal() anomaly Stephen Sprunk <stephen@sprunk.org> - 2012-08-02 00:55 -0500
        Re: signal() anomaly Ike Naar <ike@sverige.freeshell.org> - 2012-08-02 07:01 +0000
      Re: signal() anomaly Öö Tiib <ootiib@hot.ee> - 2012-09-08 20:53 -0700
  Re: signal() anomaly Nobody <nobody@nowhere.com> - 2012-08-01 18:06 +0100
    Re: signal() anomaly Tim Rentsch <txr@alumni.caltech.edu> - 2012-09-07 13:44 -0700
  Re: signal() anomaly Kleuske <kleuske@nowhere.net> - 2012-08-02 20:52 +0000

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